The present invention relates to the synthesis of diamond single crystal expected to be used in various techincal fields such as a high-temperature semiconductor device, ultraviolet laser diode or transparent protective single crystal film excellent in hardness.
Synthetic diamond has been used as abrasive grains or cutting tools due to its high hardness, and as a heat sink for a laser element due to its excellent thermal conductivity. Since the diamond exhibits big band gap, it is expected to be used as a semiconductor ultraviolet laser or emitting source, too. Recently, the applicability of the diamond has been researched in the fields of optoelectronics, high-temperature semiconductor devices or the like suitable for high-speed data processing with high-density.
According to a conventional method, such synthetic diamond is produced by heating a mixture of graphite with a catalyst in a high-temperature diamond stable zone at a high pressure. The catalyst used in this method is a Group-VIII transition metal or its alloy having the function to melt the graphite in the diamond stable zone and to precipitate diamond particles having small solubility.
Synthetic diamond may be produced by synthesizing a quasi-diamond thin film on a substrate from the mixed gas of hydrocarbon with hydrogen or by photodissociating hydrogenated carbon gas to polycrystalline or nanocrystalline thin film.
Synthetic diamond obtained in any of the conventional methods contains impurities in fairly large amount, since it is inevitable to inhibit the inclusion of dissimilar components from the atmosphere. The product is of polycrystalline structure or nanocrystalline aggregate, too. Consequently, the obtained synthetic diamond does not satisfy the requirement necessary as the semiconductive or photosemiconductive material which must have crystallinity highly controlled.